For me, it is Kawasaki's spiral shell -- I love it because it is such an ingenious model. It feels like fun folding it... and I can produce a semi-realistic, 3D model in not too much time. Some of the more complex models just feel too much like work for me some times.

The other model I enjoy folding is Yoshizawa's butterfly, because it is so simple, yet produces something that's instantly recognizable, and captures the spirit of a butterfly so well.

I think I enjoy both of these models because they are fun, clever, can be folded in a short period of time, and they make great gifts for people.
What are your favorite models to fold? Please include pictures if you can!
